TRUSTREP Sintesi della relazione

Final Activity Report Summary - TRUSTREP (Creation and Use of Trust in Virtual Communities through Reputation Management)

The aim of this project has been to examine the creation and use of trust in virtual communities through the application of reputation management systems. A reputation management system typically collects information about the past behaviour of a user to construct a reputation value that signifies how honest and good the user has been in their interaction with other members of the community. It assumes that users who have behaved honestly in the past (and thus have a higher reputation value) are more likely to behave honestly in the future. However, collecting information about past transactions can be difficult if the outcome of the transaction is not publicly visible. A user reporting on their own behaviour is considered to be unreliable. An alternative is for users to report on the behaviour of their transaction partner. But this is also problematic as dishonest users may lie about the behaviour of their partners in order to obscure their own bad behaviour. Further, in a decentralized system, there is no single trusted site to store the reputation information and it must be stored by members of the community. This adds another source of error and manipulation. Existing reputation management systems use a variety of techniques to address these issues.

We have used mathematical analysis and modelling as well as simulation of reputation management systems to study both the theoretical and the actual effectiveness of reputation management in creating trust in a virtual community. We model three different types of participants: 1) honest users who always behave correctly, 2) malicious users who behave in an unpredictable fashion and generally wish to harm the community and 3) rational users who wish to maximize their own gain even if their actions are harmful to the community as a whole. We show that a reputation management system can be used to align the goals of rational users with those of the virtual community thus increasing the overall benefit to the community. Our simulations were performed largely on the ROCQ reputation management system that was developed by the Fellow previously and improved upon in the course of this fellowship.

The results from this research include a determination of the maximum probability of a user being misclassified (classified as honest when dishonest and vice-versa) by a reputation system. We also show using game theoretic methods that in the absence of a reputation management system, the rational choice for a selfish user is to cheat every time as that will maximize their own benefit. This is true regardless of whether the community comprises only rational users or a mix of rational, honest and malicious users. We then show how the introduction of a reputation management system can change the optimal strategy for a rational user to one in which they co-operate and do not cheat. Moreover, the reputation system can also identify malicious users so that a rational user can discriminate and only interact with honest and rational users.

The theoretical results from this research are supported by simulation showing what the optimal strategy for a rational user should be in a virtual community with no reputation management, an idealised perfect reputation management system, an imperfect reputation management system and the ROCQ reputation management system. We found that rational users were induced to cooperate by reputation management systems with their cooperation almost absolute in a perfect reputation management environment and very high in mildly imperfect reputation management systems and the ROCQ reputation management system. Finally, we implement a reputation management scheme for collaborative content distribution and show that it significantly reduces the proportion of fake and corrupted content that is distributed in the network.

Reported by

THE PROVOST, FELLOWS AND SCHOLARS OF THE COLLEGE OF THE HOLY AND UNDIVIDED TRINITY OF QUEEN ELIZABETH NEAR DUBLIN.(HEREINAFTER CALLED TCD)